The present invention relates to a method for quality control of an analyzing system that makes use of a portable analyzer with insertable single-use cartridges whose sample chamber contains optical and/or electrochemical sensors, in particular sensors which are designed for determining clinically relevant parameters (pH, pCO.sub.2, pO.sub.2), ions (e.g., Li.sup.+, Na.sup.+, K.sup.+, Mg.sup.++, Ca.sup.++, Cl.sup.-), and enzyme substrates (e.g., glucose, lactate, urea) in biological fluids.
Following is a definition of some major technical terms of the invention in order to facilitate comprehension.
Analyzer: Measuring instrument based on optical and/or electrochemical sensors for measurement of samples (blood samples, for instance).
Portable analyzer: Point-of-care measuring instrument based on optical and/or electrochemical sensors. The sensors are incorporated in single-use cartridges which are inserted into the analyzer for sample measurement and discarded after the measuring process.
Sensor: Optical or electrochemical measuring element determining the concentration or partial pressure of at least one chemical component dissolved in a fluid. Several sensors may be used for simultaneous determination of the concentrations or partial pressures of different chemical components.
Simultaneous measurement: The sensors of a sensor bank are contacted with the medium to be measured (calibrating medium, control liquid, sample) during one and the same step of the process. Detection of the measuring signals need not take place simultaneously.
Single-use cartridge: A part which may be brought into contact with a portable analyzer by mechanical as well as electrical and/or optical means, featuring at least one sample chamber and sensors that are in at least indirect contact with this chamber. The single-use cartridge is designed for measurement of a single sample.
Conditioning: Temporary contact of the sensors with a given medium in order to obtain a stable sensor characteristic. Upon contact with aqueous or moist gaseous media, dry-stored sensors exhibit a characteristic that is changing over time. A similar effect is produced, in particular with sensors based on ion-permeable materials, by the diffusion-induced exchange of chemical components with aqueous media of different composition.
Sensor characteristic: Functional relationship between the concentration (or partial pressure) of a chemical component contained in an aqueous solution (independent variable) and the magnitude of a measurable optical or electrical signal of an optical or electrochemical sensor.
Calibration: Determination of the sensor characteristic.
One-point calibration: Calibration at an expected value of the quantity to be measured. For the purpose of calibration the signal must usually be obtained at two or more values of the quantity to be measured. If the functional relationship described by the characteristic is at least partially known, however, as in the instance of batchwise determination during manufacture or reproducible manufacturing, it will usually suffice to obtain the signal at a single value of the quantity to be measured in order to obtain complete calibration.
Calibrating medium, calibrating liquid: Aqueous solution or gaseous mixture containing at least one chemical component to be determined by means of a sensor bank, the concentration or gas partial pressure of this component being known and corresponding to an expected value of the respective chemical component(s) in the given measuring situation.
Quality control: Simultaneous determination of the concentrations of dissolved chemical substances and/or gas partial pressures of a quality control liquid by means of a sensor bank (for example, a single-use cartridge), and subsequent comparison of instantaneous and target values.
Quality control liquid: Aqueous solution supplied in a container (preferably made of glass) preferably impermeable to gases (such as O.sub.2, CO.sub.2, N.sub.2), water, and chemical substances that are soluble in aqueous systems, which is treated with a gas of known composition and contains various chemical components of a liquid specimen to be measured by means of a sensor bank, the concentration of these components corresponding to an expected value of the measurement variable in the given measuring situation.
Specimen: Fluids (for example, biological fluids, such as whole blood, serum, urine). Concentrations or gas partial pressures of the components to be determined are essentially unknown.
Sample: Random sample of the specimen.
Sample measurement: Simultaneous determination of the concentrations and/or gas partial pressures of the chemical substances dissolved in a sample by means of a sensor bank (such as a single-use cartridge).
In clinical laboratories various analyzers are used for in-vitro analyses of biological fluids (blood, urine, plasma, serum). The instruments mostly are based on electrochemical sensors which are calibrated at one or more expected values of the quantities to be measured, by means of liquid and gaseous calibrating media provided in the instrument, before the actual measuring process takes place. For calibration of the individual sensors, various liquid and gaseous calibrating media are employed.
It is often necessary to check accuracy and reliability of such measuring systems by means of quality control liquids. These liquids are aqueous, saline, pH-buffered solutions treated with a gas of known composition of O.sub.2 and CO.sub.2 and supplied in sealed glass containers. These liquids may contain various additives to increase gas solubility, tensides to increase wettability, and biocides to prevent biological activities. Quality control liquids preferably are used for simultaneous control of all sensors contained in the instrument; their chemical composition is distinct from that of the calibrating media used.